1. Technical Field
The present invention relates to an electrostatic image developing toner used for developing an electrostatic latent image formed by an electrophotographic process, an electrostatic recording process or the like, with a developer, a production process of the toner, a resin particle liquid dispersion usable as the raw material of the toner, and a production process of the liquid dispersion. The present invention also relates to an electrostatic image developer using the electrostatic image developing toner, and an image forming method.
2. Related Art
At present, a method of visualizing image information through an electrostatic image by an electrophotographic process is being utilized in various fields. In the electrophotographic process, an electrostatic image is formed on a photoreceptor through electrostatic charging and exposure steps, and the electrostatic latent image is developed with a developer containing a toner and then visualized through transfer and fixing steps. The developer used here includes a two-component developer comprising a toner and a carrier, and a one-component developer using a magnetic toner or a non-magnetic toner solely. The toner is generally produced by a kneading and pulverizing production process where a thermoplastic resin is melt-kneaded together with a pigment, an electrostatic charge control agent and a releasing agent such as wax and after cooling, the kneaded material is finely pulverized and then classified. In such a toner, an inorganic or organic particle is sometimes added to the toner particle surface, if desired, so as to improve flowability or cleaning property.
In recent years, a duplicator, a printer and a complex machine thereof with a facsimile or the like, each employing a color electrophotographic process, are becoming remarkably popular. In the case of realizing appropriate gloss in the reproduction of a color image or transparency for obtaining an excellent OHP image, it is generally difficult to use a releasing agent such as wax. Accordingly, a large amount of oil is applied to a fixing roll so as to assist the separation, but this causes tacky touch of a duplicated image including an OHP image, makes it difficult to write on the image with a pen or often gives a non-uniform gloss texture. In the case of a normal black-and-white copy, it is more difficult to use a wax generally employed, such as polyethylene, polypropylene and paraffin, because the OHP transparency is impaired.
Even if, for example, transparency is sacrificed, in the conventional process of producing a toner by a kneading and pulverizing method, the toner can be hardly prevented from being exposed to the surface and on use as a developer, there arises a problem such as significant deterioration of flowability or filming on the developing machine or photoreceptor.
As a method for fundamentally solving these problems, a production process by a polymerization method has been proposed, where an oil phase comprising a monomer working out to a raw material of a resin, and a colorant is dispersed in an aqueous phase and then directly polymerized to form a toner, thereby enclosing the wax inside the toner and preventing exposure to the surface.
In the above-described electrophotographic process, for providing a high-quality image and stably maintaining the toner performance under various mechanical stresses, it is very important to select the pigment and releasing agent, optimize the amounts thereof, prevent the releasing agent from exposure to the surface, optimize the resin properties to improve the gloss and releasability without a fixing oil, and suppress the hot offset.
On the other hand, a technique for enabling fixing at a lower temperature is demanded in order to reduce the energy consumption and in particular, it is recently required to stop energizing the fixing machine except for the operating time so that thorough energy saving can be attained. Therefore, the temperature of the fixing machine must be instantaneously elevated to the working temperature upon energization. In this respect, the heat capacity of the fixing machine is preferably as small as possible but if the case is so, the fluctuation width of the temperature of the fixing machine tends to be larger than ever. That is, the overshoot of the temperature after start of energization increases, and the temperature drop due to passing of paper also increases. Furthermore, when paper in a width smaller than the width of the fixing machine is continuously passed, the temperature difference between the paper passing part and the paper non-passing part becomes large. Particularly, in the case of use in a high-speed duplicator or printer, such a phenomenon is more liable to occur because the capacity of the power source tends to run short. Accordingly, an electrostatic image developing toner which can be fixed at a low temperature but is free from generation of offset until a higher temperature region, that is, which has a wide fixing latitude, is strongly demanded.
As for the technique of lowering the fixing temperature of the toner, there is known a method where a polycondensation-type crystalline resin showing a sharp melting behavior with respect to the temperature is used as the binder resin constituting the toner. However, a crystalline resin is generally difficult to pulverize by a conventional method and cannot be used in many cases.
Also, for the polymerization of a polycondensation-type resin, the reaction must be performed for a long time of 10 hours or more at a high temperature exceeding 200° C. under highly reduced pressure with stirring by the use of a large force, and this incurs massive energy consumption. In addition, a huge equipment investment is often required for obtaining durability of the reaction equipment.
In the case of producing a toner by an emulsion polymerization and aggregation method as described above, the polycondensation-type crystalline resin after polymerization may be emulsified in an aqueous medium to form a latex and then aggregated in this state with a pigment, a wax and the like, followed by fusing and coalescence.
However, the emulsification of the polycondensed resin requires an extremely inefficient and highly energy-consuming step, for example, a step of emulsifying the resin under high shearing at a high temperature exceeding 150° C. or a step of dissolving the resin in a solvent to attain a low viscosity, dispersing the solution in an aqueous medium and then removing the solvent.
Also, at the emulsification in an aqueous medium, a problem such as hydrolysis can be hardly evaded, and the material design inevitably encounters generation of an uncertain factor.
These problems are prominent in a crystalline resin but not limited to a crystalline resin and the same also occurs in the case of a non-crystalline resin.